In conventional analog plain old telephone service (POTS) telecommunications systems, it is known to provide to domestic and business users a set of services known as Custom Local Area Special Services (CLASS), whereby a subscriber can access or control functionality provided by a central office switch for obtaining information or for configuring a subscriber line. CLASS services emulate services known as "network services" often provided on a conventional PBX. In some cases these are accessed by a subscriber dialing pre-defined key sequences on his or her telephone handset. In other cases such services are bought services which are automatically generated by a service provider. Examples of such services include:
calling line identification--a facility by which a subscriber can identify a phone number of an incoming call. PA1 Integrated voice mail--where a CLASS feature is used to provide an indication of voice mail waiting. PA1 receiving service signals describing the services on a the voice band channel; PA1 receiving a call set up signal on a digital channel; PA1 transmitting the call set up signal over a wireless link; PA1 delaying the service signals for a delay period; and PA1 transmitting the service signals over the wireless link after the delay period. PA1 detecting a call set up signal received on a digital path of the subscriber line; PA1 transmitting the call set up signals over a digital channel of a wireless link of the subscriber line; PA1 receiving a set of service signals on the voice band channel of the subscriber line; PA1 storing the service signals at the base station; and PA1 after a delay period, transmitting the service signals over the wireless link of the subscriber line. PA1 receiving a digital call set up signal over an out of voice band digital path of the subscriber line; PA1 receiving the service signals over a voice band path of the subscriber line; PA1 transmitting the digital call set up signals and the service signals over a digital channel of a fixed wireless access link of the subscriber line. PA1 receiving a digitized signal over a digital channel of a fixed wireless access link, the digitized signal comprising a digital call set up signal and a digitized service signal; PA1 transmitting the digital call set up signal along a digital channel of the subscriber line; PA1 converting the digitized service signal to analog format; and PA1 transmitting the analog service signal over an analog channel of the subscriber line. PA1 transceiver means capable of receiving a digital signal comprising a call set up signal and a digitized service signal; PA1 a digital to analog converter capable of converting the digitized service signal to analog service signal format; and PA1 transmission means for transmitting the analog service signal in a voice band of an analog channel of a subscriber line. PA1 transceiver means capable of receiving a digital signal comprising a call set up signal and a digitized service signal and capable of transmitting the call set up signals and the service signals over a wireless link; and PA1 data storage means capable of storing the digitized service signals PA1 wherein the data storage means operates to store the service signals prior to transmission of the service signals over the fixed wireless access link .
Such services are specified in ITU international standard V5.2 (International Telecommunications Union ITU-T Recommendation V5.2, available from ITU Sales and Marketing Service, Place de Nations, CH-1211 Geneva 20, Switzerland, E-Mail Sales@itu.com). Various types of central office switches produced by different manufacturers may also support different selections of CLASS services, the selections differing from proprietor to proprietor. For example, Nortel Limited (Northern Telecom) specify proprietary CLASS services in their DMS-X specification, which are supported by Nortel DMS type switches available from Nortel Limited (Northern Telecom).
Referring to FIG. 1 herein, there is illustrated a prior art central office switch 100 comprising part of a prior art broad band network, the switch communicating with an item of customer premises equipment 101, over a hard wired transmission line 102, for example a coaxial cable or twisted copper wire pair, the customer premises equipment supporting a plurality of analog terminal equipment 103, e.g. subscriber handsets. Between each subscriber handset and the central office switch there exists a subscriber line 105 comprising a voice band channel which operates to carry voice or modem traffic, typically within a band of 300 Hz to 3400 Hz, and an out of voice band signaling channel which carries call set up signals, typically in the range 3800 Hz to 4200 Hz. The transmission line 102 supports a large number of such subscriber lines between the central office switch 100 and the plurality of subscriber handsets 103. Between the corresponding subscriber handsets 103 and the customer premises equipment 101, each subscriber line comprises an analog channel which carries voice band data, and a digital channel which carries out of voice band signaling data. Between the central office switch and the customer premises equipment, the analog data, e.g. voice and/or modem traffic, is digitally encoded by the central office switch and is sent down a multiplexed digital link of the transmission line 102 so producing a virtual analog data channel, for carrying in band voice/modem data. On reaching the customer premises equipment the voice band data is sent over an analog channel to the subscriber handset 103. Thus, for each subscriber line between central office switch and subscriber handset there exists an in voice band analog data channel and aft out of voice band signaling channel.
In the following example, operation of CLASS signals giving caller number identification will be given. To connect a call between an A party caller 104 having first telephone number 01803 682784 and a B party 103 having second telephone number 0171 380 2992 over a subscriber line, the B party subscriber handset receives digital call setup signals over an out of voice band digital signaling channel of a subscriber line. An associated voice band channel, over the same subscriber line carries voice and/or modem traffic once call set up has been established. Communication between the central office switch and the customer premises equipment on transmission line 102 is represented schematically in FIG. 2 herein and comprises a serial burst of messaging commands in accordance with a standard protocol, e.g. V5.2 or a proprietary protocol for example DMS-X. In a first time slot 200, the messaging commands operate to provide to the customer premises equipment 101 information describing in which time slots of a plurality of time slots 201, information corresponding to a voice band channel of the subscriber line is to be carried. For example, the V5.2 or DMS-X protocols may specify that in voice band data corresponding to a subscriber line telephone number 0183 682784 is being carried in a particular time slot within the plurality of time slots.
The customer premises equipment interprets this message and proceeds to ring the connected subscriber telephone handset corresponding to number 0171 380 2992, and generates ringing tone signals at the particular subscriber telephone, connecting the voice band signals of the specified time slots to the handset of that number over the corresponding analog channel.
The conventional set of CLASS services make use of the parallel voice band channel between the central office switch 100 and the customer premises equipment 101 immediately after call set up. Whilst the central office switch 100 and the customer premises equipment 101 are making a connection using the out of band digital channel between the central office switch and the network access equipment and ringing a subscriber telephone handset, CLASS services are sent contained in modem bursts in band via the voice band channel. Signals representing calling line identification, and other CLASS services are sent in band along the voice channel to the customer premises apparatus whilst the subscriber handset is ringing, and before A party to B party connection is made. CLASS signals are sent from the customer premises equipment 101 to the subscriber analog telephone handset 103 before, during or after an A party to B party connection is set up. Typically, the analog user handset may indicate to a user that a service is available, e.g. calling line identification by a flashing light at the user handset.
As shown in FIG. 3 herein, CLASS services may be forwarded by the customer premises equipment to the analog subscriber handset, in band in analog format in intervals between bursts of analog ring tone signals. For example, in FIG. 3, between analog ring tone signals 301, there are modem bursts carrying CLASS signals 303, e.g. a signal containing information that a calling line's identification number is 0183 682784. The modem burst is decoded by the analog handset and may be used to generate a liquid crystal display of caller number at the handset. By the above mechanism, CLASS services, similar to those provided in conventional digital handsets over hard wired transmission lines may be made available to CLASS compatible analog handsets.
Large amounts of legacy access networks exist where central office switches are connected with access network apparatus by such hard wiring, e.g. coaxial cable, or twisted wire pairs. However, deployment of such an access network is expensive, due to the installation of the hard wiring cables between the customer premises and the domestic or business premises. Typically, such hard wiring is carried on overhead telegraph poles, or in underground trenches or conduits. Trenching costs for installation of new hard wiring may typically be of the order of $100 per meter, and installation of new hard wiring may involve considerable disruption in a neighborhood. As an alternative to hard wiring between the access network apparatus and domestic/business premises, it is known to install a fixed wireless access (FWA) system (otherwise known as fixed radio access FRA or wireless local loop WLL) in which the central office apparatus communicates with network terminal equipment at subscriber premises via a wireless link. As illustrated schematically in FIG. 4 herein, a network terminal equipment radio transceiver 400 at a subscriber's premises communicates with a radio base station 401 which provides cellular coverage over typically a 5 to 20 kilometre radius in urban environments. The wireless link typically operates at a 3.5 GHz centred frequency band. Each base station is connected to a central office switch via a back haul link comprising a conventional hard wired transmission link, microwave link or fibre optic cable link.
However, whilst the fixed wireless access link provides a cost effective replacement for hard wiring in the access network, the conventional fixed wireless access link does not provide support for CLASS services.